I think that a good example of dramatic irony in Macbeth is when King Duncan comes to the castle of the Macbeths for a visit to celebrate Macbeth's elevation to Thane of Cawdor and the audience knows that the king is going to be murdered, but the king has no idea.
The king does not know that he has walked into a trap. The Macbeths have a lovely party, Lady Macbeth especially, pays respect to the king, honors the king and celebrates with him. She tells her husband that they must not reveal from their facial expressions or their demeanor any of their plans for later that night. She tells him:
Lady Macbeth: Your face, my thane, is as a book where men
May read strange matters. To beguile the time,
...look like the innocent flower,
But be the serpent under't. (Act I Scene V)
Macbeth is a villain in my view, he grabs the opportunity to be king with both hands. He kills the king, even though he is having second thoughts. His failure to resist temptation, as illustrated by the witches prophecy, result in the total corruption of Macbeth's personality, the forfeiture of his soul and his total destruction.